Device for transmission of electric power with large frequency range



Oct. 20, 1959 G. A. E. MATTSSON' 2,999,737

DEVICE FOR TRANSMISSION OF ELECTRIC POWER WITH LARGE FREQUENCY RANGEFiled Feb. 17, 1955 f/v vlsw 7'0 603779 Hug/v [1/5/97 Mnrrsro/vHrroR/vA-Y United States Patent DEVICE FOR TRANSNIISSION OF ELECTRICPOWER WITH LARGE FREQUENCY RANGE Gosta Allan Evert Mattsson, Spanga,Sweden, assignor to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden,a corporation of Sweden Application February 17, 1955, Serial No.488,953

Claims priority, application Sweden February 22, 1954 2 Claims. (Cl.333-96) The present invention relates to a device for transmittingelectric power with large frequency range.

A device according to the invention comprises a coaxial cable and ischaracterized by the inner conductor of the coaxial cable being dividedinto a number of sections arranged concentrically in succession andconnected to each other by means of condensers.

Another characteristic feature of a device according to the invention isthat the length S of the said sections, measured in kilometers, and thecapacitance C of the two condensers, measured in farads, satisfy therelation 4X1 1 X S where l is the inductance of the coaxial cable,measured in henry/km., and r is the resistance of the coaxial conductor,measured in ohm/km.

A further characteristic feature is that the inner conductor of thecoaxial cable is tubular.

The invention will be described more closely in relation to theaccompanying drawing, in which Fig. 1 is a schematic View of a deviceaccording to the invention and Fig 2 shows one of the sections of thecoaxial cable comprised in a device according to Fig. 1.

In the device according to Fig. 1, 1 is the outer conductor of a coaxialcable, the inner conductor of which is divided into a number of sections21, 22, 23 arranged concentrically and connected to each other by meansof condensers 31, 33

The length S of each one of the sections 21, 22, 23 measured inkilometers, is chosen in such a manner in relation to the capacitance Cof the condensers 31,

32 measured in farads, that these magnitudes satisfy the relation 4 lrXS in which lis the inductance of the coaxial cable, measured inhenry/km., and r is the resistance of the coaxial cable, measured inohm/km.

As appears from Fig. 1 the inner conductor of the coaxial cable, i.e.the sections 21, 22, 23 is tubular, which has proved especially suitablefor this kind of device.

In Fig. 2 a suitable shape for a section comprised in a device accordingto Fig. 1, is shown. The outer and inner conductors of the coaxialcables are referred to as 1 and 22, respectively. To obtain a goodstability the inner conductor 22, which is made of copper, silver oranother conducting material, is applied onto an inner supportingmaterial 3 and insulated from said supporting material by means of aninsulating layer 4. To fix the inner conductor relatively the outerconductor there are at suitable intervals a number of spacers 5 of someinsulating material. The space between the inner and the outer conductoris filled with suitable di-electric material, such as air or some othergas.

It is naturally also possible to make a coaxial cable without the innersupporting material and with some kind of thermoplastic substanceinstead, such as polyethylene, polystyrol etc., either homogeneous ormixed with air or some other gas to form a foamy material.

A considerable advantage of a capacitively series loaded coaxial cablewith tubular inner conductor is, that its characteristic impedance, theimage impedance, has a very simple form, since it is possible to compareits characteristic for a very large frequency range with a resistance inseries with a condenser. This entails, that if the cable is terminatedby such a simple two-pole network, its working properties become equalto its image properties, independent of the length of the cable.

The capacitive series impedances may at the amplifying stages usually beincluded in the connecting condensers of the amplifier, as well on theinput as on the output side, whereby the capacitance should be equal tothe double value of the capacitance of the other condensers of thecoaxial cable. v

As example of the dimensioning of the condensers comprised in a coaxialcable the following figures may be mentioned: At a distance S=1 km.between the condensers their capacitance C for a certain cable typeshould be 1.0,u.f.; at 8:35 km., C should be 0.3 ,uf.

I claim:

1. A coaxial cable for transmitting electric energy having a Widefrequency band, said cable comprising a tubular outer conductorcontinuous for the length of the cable, and a coaxially disposed innerconductor, said inner conductor being in form of alternately disposedconductive sections and capacitance means all connected in series, thelength of said conductive sections and the capacitance of saidcapacitance means being in accordance with the equation:

'VXS wherein S is the length in kilometers, C the capacitance in farads,l the inductance of the cable in henry/km. and r the resistance of thecable measured in ohm/km.

2. A coaxial cable according to claim 1 wherein said inner conductor iscomposed of alternately disposed tubular conductive sections allconnected in series with the capacitance means.

References Cited in the file of this patent UNITED STATES PATENTS248,742 Henck Oct. 25, 1881 2,183,123 Mason Dec. 12, 1939 2,274,346Roosenstein Feb. 24, 1942 2,796,463 Mallinckrodt June 18, 1957

